The present invention relates to transseptal catheterization, and more specifically relates to a needle assembly for transseptal catheterization, the needle assembly including an adjustable anchor point for anchoring a dilator with respect to a needle cannula.
The human heart contains four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. The right atrium is in fluid contact with the superior vena cava (SVC) and the inferior vena cava (IVC). The right atrium is separated from the right ventricle by the tricuspid valve, while the left atrium is separated from the left ventricle by the mitral valve. The right atrium and left atrium are separated by the interatrial septum, while the right ventricle and left ventricle are separated by the interventricular septum.
There are a multitude of therapeutic and diagnostic procedures in which a catheter is passed within a guide sheath or over a guide wire to access the chambers of the heart. The right atrium can be accessed from the superior vena cava or inferior vena cava. The right ventricle can be accessed from the right atrium. The left ventricle can be accessed from the aorta. The left atrium can be accessed directly from the left ventricle (through the mitral valve); however, such an approach is relatively difficult maneuver due in part to the tortuous path that must be navigated with the catheter. Such a maneuver is problematic for various reasons, including a bleeding risk and a clotting risk to the patient (because it is the arterial side, it has a relatively high pressure, which exacerbates such risks). In addition, this approach may cause arrhythmias. Therefore, another approach for accessing the left atrium was developed. In this approach, a small hole is placed in the interatrial septum, so that the left atrium can be accessed from the right atrium. This hole is typically created by a needle puncture and is referred to as transseptal catheterization.
In the standard transseptal catheterization procedure, three separate tools are involved: a sheath with a sheath hub, a dilator with a dilator hub, and a needle assembly including a cannula, a needle hub and a stylet. The stylet is usually a small, guidewire-like device that is threaded through the needle cannula and attaches to the needle hub proximally. The distal tip of the stylet extends beyond the distal tip of the needle. The distal section of the needle has a shoulder or tapered section that corresponds with an internal taper at the distal tip of the dilator. When the needle is fully inserted into the dilator, the needle shoulder functions as a hard stop that limits the distance that the tip of the needle can exit from the dilator.
The typical transseptal procedure entails numerous steps. First, right femoral vein access is gained via the Seldinger technique. Second, a guidewire is passed through introducer sheath, which was placed in the first step, into the femoral vein and threaded up the IVC to the SVC. Third, a sheath and dilator assembly is maneuvered to the SVC by being passed over the guidewire. Fourth, the guidewire is removed. Fifth, the needle assembly, usually including the stylet, is advanced through the inner lumen of the dilator until the distal tip of the needle (or stylet) is just proximal of the distal tip of the dilator. Sixth, the stylet, if present, is removed, and the needle is advanced until the tip of the needle is just proximal of the distal tip of the dilator. Seventh, the dilator/sheath/needle assembly is pulled caudally until the distal tip of the dilator is just resting on the fossa ovalis, which is a relatively thin area in the interatrial septum. Eighth, the needle is advanced forward through the dilator to puncture the septal wall (fossa ovalis). Ninth, and finally, the sheath and dilator assembly is fed through the septal wall over the needle, thereby gaining access to the left atrium.
One risk associated with transseptal needle use is inadvertent exposure. The sheath/dilator assembly and transseptal needle assembly are usually not interlocking. Thus, the needle assembly can freely translate and rotate within the sheath/dilator assembly. This freedom of movement means that the position of the needle assembly in relation to the sheath/dilator assembly must be manually maintained by the user. In particular, during the needle insertion step and the subsequent navigation of the tip of the sheath/dilator/needle assembly to the fossa ovalis, if the translational position of the needle assembly is not controlled or monitored, there is a risk of inadvertent exposure of the stylet and/or needle tip. The maintenance of needle position in relation to the dilator is especially challenging for inexperienced users. These issues can be exacerbated by the existence of multiple manufacturers of sheaths/dilator assemblies and needle assemblies; each manufacturer can have multiple different lengths of each. Therefore, if a user uses a particular dilator with a non-matched needle length or with a needle from a different manufacturer, for instance, the needle tip or stylet may inadvertently extend from the dilator. Inadvertent exposure can result in damage to the vascular and cardiac walls, which could further result in generation of potentially dangerous emboli.
Moreover, because there can be three or more lengths of sheaths/dilator assemblies/kits that the clinician can use for the procedure and there are different manufacturers of the sheath/dilator kits, each sheath/dilator assembly has a slightly different overall length and handle geometry, each length of sheath/dilator assembly requires a transseptal needle of the same length and/or manufacturer. In order to accommodate this, a hospital has to carry a larger and more varied inventory and the staff has to be sure to pull the correct needle for each procedure.
In the standard transseptal procedure, in order to mitigate this risk, the physician performs a measurement ex vivo to determine the point at which the stylet and/or needle tip is unexposed and just proximal of the dilator tip. To do this, the physician first inserts the needle fully into the dilator so that the stylet and/or needle tip exits the dilator. Next, the physician withdraws the needle proximally so that the stylet and/or needle tip is no longer exposed. At this point, the physician measures how far the needle handle is proximally offset from the dilator hub. Generally, this offset distance is “two-finger-widths” if the stylet is connected to the needle and “one-finger-width” if the stylet has been removed. This is an imprecise and non-standardized measurement that adds an extra step to the procedure. In addition, when the needle is inserted into the dilator and sheath assembly, which has been placed previously in vivo and in the SVC, the physician has to take care that the needle does not advance beyond the offset distance that had been previously measured.